This invention relates generally to a connecting rod for an internal combustion engine, and particularly, to a variable length connecting rod that can vary a compression ratio of the engine.
The xe2x80x9ccompression ratioxe2x80x9d of an internal combustion engine is defined as the ratio of the volume in a cylinder above a piston when the piston is at bottom-dead-center (BDC) to the volume in the cylinder above the piston when the piston is at top-dead-center (TDC). The higher the compression ratio, the more the air and fuel molecules are mixed and compressed resulting in increased efficiency of the engine. This in turn results in improved fuel economy and a higher ratio of output energy versus input energy of the engine.
In conventional internal combustion engines, however, the compression ratio is fixed and thus the compression ratio cannot be changed to yield optimal performance. Accordingly, variable compression ratio (VCR) internal combustion engines have been developed to vary the clearance volume of a cylinder in order to achieve improved fuel economy and increased engine power performance.
One known system for changing the compression ratio of an engine utilizes a connecting rod whose effective length can be varied. Those skilled in the art will recognize that varying the effective length of a connecting rod allows the compression ratio of an associated engine cylinder to be varied. In particular, the apparatus includes a bearing retainer disposed between a connecting rod and a corresponding crankpin, the bearing retainer has an inner surface in communication with the crankpin and an outer surface in communication with the connecting rod. The connecting rod is axially movable relative to the bearing retainer along a longitudinal axis of the connecting rod to effect a selective displacement of the connecting rod relative to the bearing retainer. The displacement causes a change in the effective length of the connecting rod and the compression ratio of the internal combustion engine. A locking mechanism is provided in cooperation with the bearing retainer and the connecting rod for maintaining the connecting rod at a selected position relative to the bearing retainer. The selected position corresponds to a selected compression ratio of the internal combustion engine. The locking mechanism is housed in an xe2x80x9cextruded portionxe2x80x9d on the side of a connecting rod. The extruded portion includes a hydraulically actuated lock pin that can engage a corresponding aperture in the bearing retainer to lock the connecting rod relative to the bearing retainer.
A problem associated with the known connecting rod is that the overall width of the connecting rod having the extruded portion for the locking mechanism is wider than a conventional xe2x80x9cconstant lengthxe2x80x9d connecting rod. Thus, to accommodate the extruded portion, clearance grooves are machined in the counterweights of the crankshaft to allow the extruded portion of the connecting rod to move therethrough. Thus, utilizing the known connecting rod requires additional machining of xe2x80x9cstockxe2x80x9d crankshafts which increases manufacturing costs and the assembly time.
The aforementioned limitations and inadequacies of conventional connecting rods are substantially overcome by the inventive connecting rod for selectively varying a compression ratio of an internal combustion engine. The connecting rod has a variable effective length and integrates a locking mechanism within the body of the connecting rod without utilizing an extruded portion for the locking mechanisms.
The inventive connecting rod includes a body portion extending along a first axis having an aperture extending therethrough generally perpendicular to the first axis and parallel to a crankpin axis. The connecting rod further includes a bearing retainer disposed in the aperture between the body portion and a crankpin of the engine. The aperture is configured to allow selective displacement of the body portion along the first axis relative to the bearing retainer. The displacement causes a change in the effective length of the body portion and the compression ratio of the engine. The connecting rod further includes a first locking mechanism contained within the aperture of the body portion and operably disposed between the bearing retainer and the body portion. The first locking mechanism has a first locking element that extends into a first gap formed between first and second opposing surfaces of the body portion and the bearing retainer, respectively, to create a first compression fit. The compression fit locks the body portion at a first position relative to the bearing retainer. The first position corresponds to a first selected compression ratio of the engine.
The inventive connecting rod in accordance with the present invention provides a substantial advantage over conventional systems and methods. In particular, the connecting rod integrates a locking mechanism within the body of the connecting rod without utilizing extruded portions to hold the locking mechanisms. Thus, the connecting rod can be utilized with conventional crankshafts with minimal additional machining being required on the crankshafts. Thus, the inventive connecting rod provides for reduced manufacturing costs and a reduction in assembly time as compared with known variable length connecting rods.
Another advantage associated with the inventive connecting rod is that the connecting rod is lighter than known variable effective length connecting rods because no extruded housings are utilized for the locking mechanisms.
Still another advantage associated with the inventive connecting rod is that the locking mechanism is compressively loaded between the body portion and the bearing retainer (i.e., creates a compression fit) to lock the bearing retainer relative to the body of the connecting rod. The compression fit results in decreased bending of the locking member as compared with known locking members having shear loading between two members of the connecting rod.